Add logarithmic functions

[Xrayez]

Adds log2, log10, and log with ability to compute logarithm with arbitrary base.

For instance, I've come up with a way to calculate number of trials in order to achieve some success rate for some probability event via script, which requires finding x in:

• 1 - (1 - p)^x:

func trials_until_success(event_probability, success_rate = 0.99):
    return GoostMath.log(1.0 - success_rate, 1.0 - event_probability)